Distribution warehouses for groceries and similar merchandise lines essentially carry out the following functions: (a) pallets of merchandise are received from individual suppliers; (b) the merchandise is stored out of the weather pending distribution; (c) portions of pallets (e.g. one or more cases of merchandise) are picked and combined with other cases to form new pallets containing a mixture of products; and (d) the mixed pallets are shipped to the retail stores.
In a conventional grocery warehouse, three types of storage are provided: (I) block storage, where pallets holding a large quantity of incoming merchandise are stacked in a storage area on top of one another as high as a fork lift truck can reach; (II) pick storage, where two or three single-product pallets are stored in a pick area on the floor or on individual shelves within the picker's reach for picking a product mix; and (III) stock storage, where two or three single product pallets are stored in the pick area on a shelf or tier above the picker's reach, for the purpose of replenishing the pick stock as it becomes exhausted.
In order to move merchandise from the receiving dock to the shipping dock, the following operations are involved in a conventional warehouse: (1) incoming pallets, which are commonly about two to four feet in height are stacked two or three high to form a pallet stack approximately six to eight feet in height, which a fork lift truck can handle as a unit; (2) the pallet stacks are moved from the receiving area to the appropriate block storage bay; (3) individual pallet stacks are moved from the block storage bay to the stock storage shelf of the appropriate pick bay; (4) individual pallets are moved from the stock storage shelf to the pick shelves or floor below; (5) the products are picked and assembled into mixed-product pallets; and (6) the mixed-product pallets are moved to the shipping area.
Because steps (1) through (4) above involve vertical movement of pallets at substantial heights above the floor, they require the use of fork lift trucks. These are expensive, cumbersome vehicles which are relatively slow and difficult to operate, and which require a great deal of maneuvering room. Inasmuch as steps (3) and (4) require the use of a fork lift truck in the pick area aisles, the minimum aisle width for the pick area of a conventional warehouse is about twelve feet.
The most common pallet size in the grocery industry is about 48 inches by 40 inches, with the height of the pallet depending on the package size of the product involved. In the block storage area, where all handling is done by fork lift truck, it is practical to store pallets 2 or sometimes even 3 deep transversely to the aisle. In the pick area, however, the reach limitation of the picker dictates storage only one pallet deep.
In the conventional warehousing system, the racks in the pick area must of necessity be supported by vertical supports or legs at fairly close intervals. In addition, the positioning tolerances for pallets handled by fork lift trucks require about 6 inches between pallets, so that the conventional system requires about 48 inches per pallet space (the long dimension of the pallet being transverse to the aisle when stored).
A conventional warehouse bay is 60 feet .times. 40 feet in size. With the 12-foot aisles of the conventional system disposed transversely to the bay, 60 pallet spaces can be accommodated by a standard bay in the conventional system. Considering the large number of different products handled by the average grocery warehouse, it is necessary to store about 50 to 60 different products, on the average, in each pick area bay if the warehouse building is to remain within a conveniently useable and economically justifiable size. Consequently, only one pallet space of the pick area can normally be allocated to any one product.
Experience has shown that the majority of products in a typical chain store warehouse are picked at the rate of about 60 to 120 cases per day. With the reach of an average man being about 6 feet 6 inches, and about 6 inches being consumed by the shelf and shelf clearance in the conventional pick storage, one pallet space of the conventional system can accommodate two pallets per tier of 40 cubic feet or less each; in other words, a total of no more than 80 cubic feet of pick storage product. This means that more often than not, the pick storage of any given product is exhausted before the end of the day, and a fork lift truck has to be called in to replenish the pick storage from the stock storage.
Aside from creating movement problems for the picker due to the fork lift's blocking the pick aisle during the replenishing operation, the conventional system often results either in a delay between exhaustion and replenishing, or in replenishing before all cases of the product have been picked from pick storage. In the latter event, when the pick storage is replenished with full pallets, leftover cases of product are frequently placed on the floor in front of the pick storage pallet, where they obstruct the aisle.
A further disadvantage of the conventional system is that the picker, who works on the floor, cannot load a mixed pallet on a cart to more than about 6 feet from the floor without exceeding his reach. Inasmuch as the bed of the cart is typically about 2 feet off the floor, the maximum mixed pallet height is about 4 feet.
Experience has shown that in a conventional warehouse, using the most efficient type of conventional picking equipment, the average picker picks on the order of 1,000 cases of product per 8-hour shift. Inasmuch as a warehouse of the size contemplated herein can accommodate no more than about 100 pickers per shift, lest they get in each other's way, the output capacity of the warehouse is about 100,000 cases per shift. It should be noted that each shift requires its own complement of machinery, as the batteries of most electrically driven warehousing machinery are designed for 8-hour work, 16-hour charge cycles.
In addition to the replenishing which is done during the regular work shifts, it is common practice in grocery warehouses to replenish the pick storage and stock storage during the night, when the fork lift operators can work without interfering with the pickers.